1. Field of the Invention
This invention relates to the field of contact lens treatment, and more particularly relates to contact lens disinfection, and especially relates to the neutralization of iodine disinfectants used to treat contact lenses. In some aspects, this invention further relates to the simultaneous cleaning and disinfection of contact lenses using iodine as the active disinfectant.
2. Description of the Related Art
Iodine is a well-known disinfecting agent known to be useful against a variety of organisms, including viruses, bacteria, spores, yeast, molds, protozoa, fungi, worms, nematodes and the like. Because of the wide range of disinfecting capabilities, iodine has been suggested for use as a contact lens disinfectant. However, iodine is a strong irritant at higher concentrations and may, when used in concentration required for disinfection, destroy animal proteins and otherwise be harmful. Therefore, because of the potential harm to the eye, iodine is preferably neutralized before the disinfected lens is inserted in the eye.
Methods disclosing the neutralization of iodine as a contact lens disinfectant are known. See U.S. Pat. Nos. 3,911,107 and 4,031,209 to Krezanoski. Both patents disclose neutralizing the iodine in solution by slow dissipation methods and use compounds suitable for human and animal use. The neutralizing solution favored by Krezanoski contains sorbic acid and EDTA.
The Krezanoski patents also disclose compounds known as antioxidants that destroy available iodine. Examples of these compounds include alcohols, aldehydes, alkenes, alkynes, aromatic hydrocarbons, amides, quinones, hydroxy acids, sugars, amino acids, sulfites, thiosulfates, sulfhydryl containing compounds, and polyunsaturated organics. Solutions of such have been found to destroy all of the available iodine at different rates. Many such compounds will be satisfactory for various industrial purposes. However, safety and tissue tolerance requirements restrict the number of compounds suitable for human and animal use.
U.S. Pat. No. 4,312,833 to Clough issued Jan. 26, 1982, also teaches a method of disinfecting contact lenses using iodine. In Clough's process, contact lenses are contacted with a solution containing iodine and a reducing agent capable of reducing the available iodine level to substantially zero in a time of at least 30 minutes and at a temperature of from 20.degree. to 25.degree. C. The iodine is present as an iodophor and the preferred organic reducing agent is sodium formate.
Amino acids have been used to neutralize iodine. Histidine is not known to have been previously suggested for use in care regimens for contact lenses, although the oxidation reaction of histidine with an excess of iodine is discussed in a paper by Schutte, L., et al, "The Substitution Reaction of Histidine and Some Other Imidazole Derivatives With Iodine," Tetrahedron, Suppl. 7, pp. 295-306 (1965). One drawback to using an imidazole such as histidine is the formation of an oxidation product that decomposes to a brown degradation product.
Schutte, L., and Havinga, E., "The Degradation Reaction of Histidine With Iodine," Recueil 86: 385-392 (1967) further investigated the I.sub.2 -degradation of histidine. By-products included carbonate, iodoform, oxalic acid, ammonia and iodide products. Additionally, they studied the reactions of some imidazole derivatives: during the iodination of histamine, the initial formation of a brown precipitate, probably a diiodo product, was observed. This dissolved in the further course of reaction. It was also suggested that histidine methyl ester follows a different reaction path as no iodoform is formed during its degradation as with the oxidation of histidine and histamine.
Alexander, N. M., "Reaction of Povidone-Iodine With Amino Acids and Other Important Biological Compounds," Proceeding of the International Symposium on Povidone, pp. 274-288 (University of Kentucky College of Pharmacy, Lexington, Ky., 1983) reports studies of the reaction of povidone-iodine with amino acids, peptides and other biological molecules. Methionine, histidine, cysteine, tyrosine and tryptophan reacted with povidone-iodine, whereas all of the other common amino acids (such as alanine, arginine, aspartic acid, cystine, glutamic acid, glycine, isoleucine, leucine, lysine, phenylalanine, proline, serine, threonine, and valine), did not react.
In addition to disinfection, the contact lens should also be cleaned of any debris. This debris is in the form of lipids, mucins and proteins that accumulates as a result of normal contact lens wear. Surfactants may remove the looser bound debris but an enzyme, or a combination of enzyme and surfactants, may be needed to remove protein which is harder to remove. Cleaning and disinfection may involve two separate steps with the cleaning occurring first but may be performed simultaneously with certain disinfectants and enzymes. Single step systems have a substantially greater compliance rate.
Another common compliance issue deals with the rubbing that typically accompanies cleaning and the rinsing that is often required to remove any residual cleaner or debris from the lens. A single step cleaning and disinfecting system with no rubbing or rinsing is the goal of many contact lens solution companies but currently, no solution succeeds in meeting all these requirements.
There are many products on the market that remove surface debris from a contact lens. Daily cleaners usually contain surfactants. Weekly cleaners usually contain proteolytic enzymes. Both types of products usually require the lenses to be rubbed and rinsed after use. With a daily cleaner, the rub and rinse occurs prior to disinfection while with the enzymatic cleaner, a rinse to remove any lens debris may occur prior to insertion of the lens into the eye.
An example of cleaning methodology requiring rubbing is provided in U.S. Pat. No. 3,907,985 to Rankin issued Sep. 23, 1975. This reference discloses an ophthalmic solution comprising an aqueous solution of polystyrene sulfonate having a molecular weight between 75,000 to 10,000,000, and preferably polyethylene glycol. The solution as disclosed provides a lubricant and cushioning effect to traumatized eyes along with providing a cleaning function. The cleaning method disclosed comprises the steps of soaking a lens in the ophthalmic solution followed by rubbing the lens between the fingers and subsequently rinsing the lens with water. Although the reference stated that the disclosed regimen cleaned debris from lenses, there was no specific description of protein removal.
Iodine is a highly effective contact lens disinfectant from the perspective of antimicrobial efficacy but iodine disinfectant systems have a tendency to discolor lenses. Performance of systems such as those disclosed by Krezanoski is difficult to control because neutralization is highly dependent on ambient light conditions. Moreover, sorbic acid can be irritating and sorbic acid solutions may have an undesirable color.
Current regimens for the care of nondisposable, soft contact lenses typically require several component products: a daily cleaner, a weekly cleaner, and a disinfectant. Regimens combining weekly cleaning and disinfecting are known, but more effective and convenient care regimens have long been sought.